First, you need the correct ingredients; this includes real Hershey's chocolate bars and Campfire brand marshmallows, preferably the super-ginormous sized variety. Now, I don't care what the Kebbler Elves say; graham crackers are graham crackers no matter the brand so, feel free to go cheap on the crackers and, that's it for ingredients.
Next, you need to build a nice, roaring fire, but; don't immediately toss your marshmallows into the flame, instead; let the fire burn down for an hour or so to provide a build-up of nice, hot coals over which to toast them.
While you're waiting, roast a couple of wieners over the flames or, you know, drink some wine.
Unless you are underage, obviously. In that case, play on a swing, preferably one that hangs from a high tree.
Or, commune with the local wildlife, you never know; you might find your prince.
Or, a frog, anyway.
Finally, when the coals are just right, gently toast your super-sized marshmallows over the fire, being careful not to burn them unless, like me; you enjoy burnt marshmallow skin, mmm, mmm, good.
When the marshmallow is perfectly toasted, squish it between two (cheap) graham crackers and a couple of squares of a Hershey's bar and, voila!
This post brought to you by a massive sugar high; you're welcome.